Some early Soviet tv sets

[Giulio Maiocco]

Hi,

well, I know quite well the KVN49-4 TV set, having restored both of the only 2 known to exist in Italy, one is mine, the other is in my friend's collection.

The circuit is a bit on the weird side, there is NO RF conversion and IF strips, simply this is a TRF receiver using the russian equivalent of the USA 6AC7 tubes. Also, there is no vertical output transformer, there is a choke loading a section of the 6N8S (6SN7GT) vertical oscillator and output. The Hor. section employs half of a 6N7S (6N7GT) as a blocking oscillator, a 807 as output tube and the other section of the 6N7S is used as a damper tube, but not recovering energy, instead short-circuiting it to ground thru 2 18Kohm resistors in parallel.

The capacitors used in these sets are of unusual high quality, paper in oil, I believe, housed in a ceramic tube with metallic caps soldered at both ends of the tube (there is a small metallisation of the tube at each end). Me being me not trusting old capacitors anyway, I replaced all of 'em.

The components are not soldered together with the usual tin-lead alloy, but instead are spot-welded, and this is quite a PITA when you have to change something

The controls on the right side of the chassis, hidden with a wooden panel are, IIRC, for hor and vert centering, vert linearity and amplitude, vert and hor sync. The slider control is the hor width that moves a laminated core in or out of an inductor wired in series to the scan coils

The KVN49-4 has only 3 channels, the selector is a lever mechanism on the back of the set.

These are interesting sets, the weak point is the CRT, that most of the times is either really gassy or completely with no emission. These sets, BTW, needs a strong CRT, the EHT only being 4,5KV

Best regards

Giulio Maiocco